Peroxy-derivative functionalization of polypropylene via solid-state shear pulverization

ABSTRACT

Functionalization of polymers, including polyolefins, via decomposition of organic peroxides through the use of solid-state shear pulverization.

This application claims priority to and the benefit of InternationalApplication No. PCT/US2013/061240 filed Sep.23, 2013, and priorprovisional patent application Ser.No. 61/704,177 filed Sep. 21,2012—each of which is incorporated herein by reference in its theentirety.

BACKGROUND OF THE INVENTION

Polypropylene (PP), a chemically resistant commodity plastic, isoccasionally functionalized with polar moieties in order to improve itscompatibility with more polar polymers and fillers in composites. Forexample, in immiscible polymer blends (e.g., PP/Nylon blends),functionalized PP can be used to obtain reactive compatibilization as aresult of in situ reaction between the polar moieties on thefunctionalized PP and the polar component of the blend (e.g., nylon).The most commonly produced (and studied) system of functionalized PP ismaleic anhydride grafted PP (PP-g-MA). Currently, commercial productionof PP-g-MA is achieved via melt processing, with PP being processed inthe presence of low levels of initiator and maleic anhydride monomer.Melt processing, however, is accompanied by drastic molecular weightreduction of PP, which in turn results in dramatic loss in materialproperties of the product as compared to that of the neat PP from whichit was made. The molecular weight reduction is caused by a free-radicalchemistry (β-scission) that is highly dependent on temperature. (SeeFIG. 1.) As processing temperature increases, the rate of β-scissionincreases dramatically (See, Rätzsch, M.; Arnold, M.; Borsig, E.; Bucka,H.; Reichelt, N. Progress in Polymer Science 2002, 27, 1195-1282 andDickens, B. Journal of Polymer Science: Polymer Chemistry Edition 1982,20, 1169-1183). Because melt processing is carried out at hightemperatures (e.g., ˜190-220° C.), the degree of β-scission andmolecular weight reduction are typically quite significant. As a result,there remains an on-going concern in the art to develop an alternate,effective process for the preparation of functionalized polyolefins.This need has been recognized and documented clearly in the researchliterature: The incorporation of functional groups along the backbone ofpolyolefins such as polyethylene and polypropylene in a selective,controlled, and mild manner is one of the most important challengescurrently facing synthetic polymer chemists. (See, Boaen, N. K.;Hillmyer, M. A. Chemical Society Reviews 2005, 34, 267-75.)

SUMMARY OF THE INVENTION

In light of the foregoing, it is an object of the present invention toprovide one or more methods for the grafting and/or incorporation ofvarious functional groups onto a polymer, thereby overcoming variousdeficiencies and shortcomings of the prior art, including those outlinedabove. It will be understood by those skilled in the art that one ormore aspects of this invention can meet certain objectives, while one ormore other aspects can meet certain other objectives. Each objective maynot apply equally, in all its respects, to every aspect of thisinvention. As such, the following objects can be viewed in thealternative with respect to any one aspect of this invention.

It can be an object of the present invention to provide one or moremethods to graft carbonyl moieties onto a polymer backbone.

It can also be an object of the present invention to provide one or moremethods to functionalize a polymeric resin using a peroxide only.

It can be another object of the present invention to provide one or moremethods for incorporation of carbonyl functional groups, via theaddition of benzoyloxy radicals, into a polymeric resin to impart one ormore functional effects thereto.

It can be an object of the present invention to provide one or moremethods for the incorporation of an organic peroxide decompositionproduct (e.g., acyloxy or alkoxy radicals), into a polymeric resin toimpart one or more functional effects to the resin.

It can be an object of the present invention, alone or in conjunctionwith one or more of the preceding objectives, to provide a polymericmaterial comprising at least one propylene monomeric unit comprising apendent carbonyl moiety—such a moiety as can undergo further reactionand/or such a polymeric material as can be used to compatibilizepolypropylene with more polar polymer and composites.

It can also be an object of the present invention, alone or inconjunction with one or more of the preceding objectives, to provide apolymeric material functionalized with carbonyl or other moieties forwhich the extent of molecular weight reduction can be controlled by thetype of post-pulverization processing

Other objects, features, benefits and advantages of the presentinvention will be apparent from this summary and the followingdescriptions of certain embodiments, and will be readily apparent tothose skilled in the art having knowledge of various polymerfunctionalization techniques. Such objects, features, benefits andadvantages will be apparent from the above as taken into conjunctionwith the accompanying examples, data and all reasonable inferences to bedrawn therefrom. In part, the present invention can be directed toward amethod of preparing a functionalized polymer. Such a method can compriseproviding a mixture comprising a polymer component and an organicperoxide; and applying a mechanical energy to such a mixture throughsolid-state shear pulverization in the presence of cooling at leastpartially sufficient to maintain such a polymer in a solid state duringpulverization. Such pulverization can be at least partially sufficientto graft a peroxy derivative onto such a polymer component and provide afunctionalized polymer.

As would be understood by those skilled in the art made aware of thisinvention, such a polymer or component thereof can have a C—H bondsusceptible to homolytic cleavage and/or reaction with a peroxidefree-radical decomposition product or derivative. Without limitation,such a polymer can be selected from polyolefins, polyesters, polyamides,epoxides, elastomers, copolymers thereof and combinations of suchpolymers and copolymers, or as would otherwise be known to those skilledin the art. In certain embodiments, such a polymer component can beselected from polyolefins, co-polymers of such polyolefins andcombinations thereof. In certain such embodiments, such a polymercomponent can be selected from polyethylene, polypropylene andco-polymers thereof.

Without limitation, and organic peroxide useful in the context of thisinvention can be selected from disubstituted peroxides of a formulaRO—OR′, where R and R′ are independently selected from alkyl, cycoalkyl,alkenyl, alkenyl, acryloyl, aryl, aroyl and acyl groups (or acorresponding ketal or hemiketal); and such a peroxy derivative can beselected from alkoxy, cycloalkoxy, alkenyloxy, alkenoyloxy, acryloyloxy,aroxy, aroyloxy and acyloxy (or a corresponding ketal or hemiketal)moieties. In certain embodiments, benzoyl peroxide can be utilized, witha peroxy derivative comprising a benzoyloxy moiety. Regardless, such anorganic peroxide can comprise about 0.01 wt % to about 10 wt % of such amixture.

With respect to any polymer component(s) utilized, such a mixture cancomprise a filler component. Without limitation, such a filler can beselected from cellulose, rice husk ash, talc, silica, modified clay,unmodified clay, modified graphite, unmodified graphite, graphene,single-walled carbon nanotubes, multi-walled carbon nanotubes andcombinations thereof, together with various other filler componentsknown to those skilled in the art made aware of this invention. Such acomponent can comprise about 0.1 wt % to about 50 wt % of such amixture, or as would otherwise needed to provide desired functionaleffect or material property.

Such a functionalized polymer can be melt-mixed and, optionally,injection molded. Regardless, such a functionalized polymer cansubsequently be incorporated into an article of manufacture.

In part, the present invention can be directed toward a method ofpreparing a functionalized polymer. Such a method can comprise providinga mixture comprising a polymer comprising a polypropylene component andan organic peroxide component; and applying a mechanical energy to sucha mixture through solid-state shear pulverization in the presence of anelement of cooling at least partially sufficient to maintain such amixture in a solid state, such pulverization as can be at leastpartially sufficient to graft a corresponding peroxy derivative ontosuch a polypropylene component and provide a polymer functionalized witha corresponding moiety. Polymer and peroxide components (and,optionally, filler components) useful in such embodiments can be asdiscussed above or illustrated elsewhere herein.

In part, the present invention can also be directed toward a method ofusing solid-state shear pulverization in the benzoyloxyfunctionalization of polypropylene. Such a method can comprise providinga polypropylene (e.g., isotactic or atactic) and benzoyl peroxidecomponent mixture; introducing such a mixture into a solid-state shearpulverization apparatus, such an apparatus as can comprise a coolingcomponent at least partially sufficient to maintain mixture solid state;and shear pulverizing such a mixture, such pulverization as can be atleast partially sufficient to graft a benzoyloxy moiety onto apolypropylene component.

In part, the present invention can also be directed compositionally to apolymer. Such a polymer can comprise polypropylene with one or aplurality of propylene monomeric units comprising a pendent benzyloxymoiety, such monomeric units as can be randomly distributed within sucha polymer, and such a polymer the solid-state shear pulverizationproduct of polypropylene and benzoyl peroxide. In certain embodiments,such a polymer product can comprise up to about 0.15 wt. % of such abenzoyloxy moiety. In certain embodiments, such a moiety can be up toabout 0.50 wt. % or more of such a polymer product. Benzoyloxy graftingpercentage can be or approach 100%. Regardless, carbonyl content can beat least partially sufficient to provide one or more functional effects,including but not limited to compatibilization of a blend ofpolypropylene with a more polar polymeric component (e.g., withoutlimitation, nylon) or composite.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: SSSP Apparatus of the sort useful in conjunction with certainembodiments of this invention.

FIG. 2: FTIR spectra of ester functionalized PP synthesized via SSSP(solid curve), ester functionalized PP synthesized via melt processing(dotted curve), and neat PP as received (dashed curve) in spectralranges of (a) 1800-1650 cm⁻¹ and (b) 750-650 cm⁻¹.

FIG. 3: Viscosity as a function of time for neat PP pellet (as received)and neat PP (pulverized). The data was collected at 180° C. using coneand plate and a 0.01 s-1 shear rate.

FIG. 4: Viscosity as a function of time for 1 wt % BPO pulverized withPP. The data was collected at 180° C. using cone and plate and a 0.01s-1 shear rate.

FIG. 5: FTIR spectra of a blend of and ODA/PP blend containing 155 μeqODA, i.e., 5 wt % ODA in ODA/PP blend, (solid curve) and neat PP (dashedcurve). The inserted molecular structure is that of octadecyl acrylate(ODA).

FIG. 6: Fluorescence spectra of 0.3 g/L solution of Pyr-MeNH₂ in xyleneat 100° C. (dotted curve) and 2 g/L solution PP-g-ES/5 in xylene at 100°C. after first being reacted with Pyr-AA and then purified six times bydissolution and precipitation to remove unreacted Pyr-AA. (Both spectrahave had emission intensity normalized to unity at the peak emissionwavelength.)

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

As relates to certain non-limiting embodiments, this invention providesa method of functionalizing PP with benzoyloxy and related carbonylgroups via solid-state shear pulverization (SSSP). Taking advantage ofunique near ambient temperature chemistries associated with SSSP, PPfunctionalization is achieved with suppressed molecular weightreduction. This carbonyl functionalized PP can be employed inapplications that would otherwise utilize PP-g-MA.

Use of SSSP in conjunction with the present invention provides severaladvantages over existing technologies, including but not limited to:

-   -   Near ambient temperature conditions associated with SSSP provide        advantages relating to chemistries that are otherwise        unattainable under melt processing conditions. In particular,        these unique chemistries enable functionalization of PP with        carbonyl groups (e.g., based on the addition of alkoxy or        acyloxy radicals that are produced from the decomposition of        organic peroxides). This type of functionalization is not        observed under melt processing conditions by virtue of the high        processing temperatures that are used.    -   Carbonyl functionalization, as achieved via SSSP, results in a        product that has the potential to undergo branching at elevated        temperatures without the use of poly-functional monomers (as is        done for branching of PP under melt conditions with organic        peroxides).    -   The near-ambient temperature conditions utilized in SSSP allow        for the suppression of β-scission during processing; this        results in the suppression of molecular weight reduction during        SSSP. On the contrary, the high temperatures used in melt        processing result in dramatic molecular weight reduction because        of the increased rates of β-scission.    -   Unlike ball milling and solvent processing, SSSP is a        continuous, industrially scalable, and high throughput process.    -   Compared to solvent processing, SSSP avoids the use of copious        amounts of hazardous solvents.    -   Relative to other processing methods, SSSP is very versatile as        a result of the ease with which product properties can be        fine-tuned by changing operating conditions (e.g., screw design,        screw speed, and zone temperatures).

As discussed below, major benefits from an SSSP apparatus employed inconjunction with the present methodologies relate to the ability to coolor maintain the barrel at a temperature sufficiently low enough toensure that the polymeric material remains in the solid state duringpulverization. These major benefits also relate to the use of tri-lobeand/or bi-lobe screw elements along a portion of the pulverizer screw.Details regarding SSSP processes and equipment (e.g., componentconstruction, screw elements, transport elements, kneading or shearingelements, and spacer elements and/or the sequence or design thereofselected or varied as required to accommodate a polymer startingmaterial, pulverization parameters and/or a resulting pulverized polymerproduct) are known to those skilled in the art made aware of thisinvention. (See, e.g., Furgiuele, N.; Lebovitz, A. H.; Khait, K.;Torkelson, J. M. Macromolecules 2000, 33, 225-228; Furgiuele, N.;Lebovitz, A. H.; Khait, K.; Torkelson, J. M. Polym Eng. Sci 2000, 40,1447-1457; Lebovitz, A. H.; Khait, K.; Torkelson, J. M. Macromolecules2002, 35, 8672-8675; Kasimatis, K. G.; Torkelson, J. M. PMSE Prepr 2005,92, 255-256; Tao, Y.; Kim, J.; Torkelson, J. M. Polymer 2006, 47,6773-6781; Walker, A. M.; Tao, Y.; Torkelson, J. M. Polymer 2001, 48,1066-1074; Lebovitz, A. H.; Khait, K.; Torkelson, J. M. Polymer 2003 44,199-206; Brunner, P. J.; Clark, J. T.; Torkelson, J. M.; Wakabayashi, K.Polymer Engineering and Science 2012, 52, 1555-1564; and U.S. Pat. Nos.5,814,673; 6,180,685; and 7,223,359—each of which is incorporated hereinby reference in its entirety.)

More specifically, in the context of this invention, SSSP is carried outin a “pulverizer,” a Model ZE 25 Berstoff twin-screw extruder modifiedwith a cooling system. The screw design for this modified extruder ismade up of two segments. The first segment is made up of spiralconveying and bi-lobe kneading elements in the first segment; the secondsegment is made up of tri-lobe shearing elements. This pulverizer has abarrel length-to-diameter ratio of 26.5. In the first segment, where thescrew elements have a diameter of 25 mm, the length-to-diameter ratio ofthe barrel is 19. The second segment has screw elements with a diameterof 23 mm and length-to-screw diameter ratio of 7.5 for the barrel. Thecooling system, which operates at −6° C., is controlled by circulating a60/40 wt % glycol/water mixture using a Budzar Industries WC-3 chiller.Such low operating temperatures allow materials to be processed in theirsolid state (i.e., below their melting or glass temperatures). Thispulverizer uses high shear and compressional forces to causefragmentation and fusion of materials. Processing in the solid-statehelps to overcome thermodynamic and kinetic limitations that may beassociated with melt processing. It also suppresses degradation thatoccurs as a result of β-scission under high temperature conditions. Aswell as being continuous, SSSP is environmentally benign and scalable tocommercial levels.

In general, SSSP is not limited to the system described above. Thecomponents for accomplishing SSSP include an extruder that is modifiedwith a cooling or heat transfer medium such that materials are retainedin the solid state during pulverization. This modification may involve,but is not limited to a cooling system and medium jacketed around thebarrel, and/or a cooled screw, and/or a heat transfer system and mediumthat operates at a temperature above room temperature and is jacketedaround the barrel. Pulverization itself is accomplished via the use ofan extruder that has bi-lobe elements or tri-lobe elements or acombination of bi- and tri-lobe elements, such that sufficient work canbe can be performed on the material in its solid-state to result in thedesired reaction.

With reference to FIG. 1, an SSSP apparatus utilizes mixing, conveying,and pulverization zones, each with a different combination of conveying,mixing, and shearing elements. The level of the applied shear stress canbe tuned by altering the type of screw applied. For example, usingreverse shearing elements results in making the screw “harsher” andincreases the residence time in the apparatus; using forward shearingelements results in making the screw less “harsh” and reduces theresidence time. The material enters as pellets but exits the pulverizerin the solid state as powder, flakes, or particulate.

To functionalize PP with benzoates and related carbonyl groups, anorganic peroxide (e.g., benzoyl peroxide (BPO)) is used as theinitiator. The resulting pulverization products were purified andpressed into thin films for Fourier Transform Infrared (FTIR)spectroscopy. The purification was done by dissolution in boiling xylenefollowed by precipitation with methanol, which has proven to be the mostreliable method of removing any unreacted maleic anhydride from thesamples. The FTIR spectra were collected at room temperature and used tocharacterize the carbonyl group functionalization of PP. To determinethe level of carbonyl grafting onto PP a calibration curve was createdusing blends of octadecyl acrylate (ODA) and PP. For all spectralanalyses, the data in the regions of interest (between 1800 and 1650cm⁻¹ and between 750 and 900 cm⁻¹) were deconvoluted into componentpeaks using a Lorentzian function. The calibration curve based on ODAwas used to quantitatively characterize the amount of carbonyl moietiesgrafted onto PP. Up to 1.14 wt % or more can be realized for pulverizedsamples.

FIG. 2, below, shows a comparison between FTIR spectra of a sample ofcarbonyl functionalized PP synthesized via melt processing (dotted line)or pulverization (bold line); it also shows the FTIR spectrum of neat PP(dashed line). The comparison in FIG. 3 shows the presence of a strongabsorbance peak for the pulverized sample at 1723 cm⁻¹ and the absenceof this absorption for melt processed sample. This peak is associatedwith absorption by ester functional groups in carbonyl groups.Pulverized samples also show distinct absorbance peaks at ˜740 cm⁻¹ as aresult of phenyl groups from the BPO used.

Unique chemistries associated with SSSP afford direct functionalizationof PP with organic peroxides by taking advantage of the temperaturedependence of peroxide decomposition. Scheme 1, below, shows thedecomposition of BPO. The process begins with the cleavage of the O—Obond to produce benzoyloxy radicals in step 1. The benzoyloxy radicalthen undergoes decarboxylation to produce phenyl radicals and releasecarbon dioxide. The second step is highly dependent on temperature andsignificantly less likely to occur under near-ambient temperatureconditions. (See, Chateauneuf, J.; Lusztyk, J.; Ingold, K. U. Journal ofAmerican Chemical Society 1988, 110, 2886-2893.) Using SSSP, it ispossible to functionalize PP with benzoyloxy, as well as other alkoxyand acyloxy radicals.

Scheme 2 shows a proposed mechanism for carbonyl functionalization ofPP. During SSSP the rate of decarboxylation (see step 2) issignificantly suppressed, resulting in a higher prevalence of benzoyloxyradicals formed in step 1 and allowing for the grafting of PP withbenzoates. However, during melt processing, the rate of decarboxylationis high resulting in a higher prevalence of phenyl radicals andsubsequently, no grafting of PP with benzoates. In the absence of step2, which should be negligible at the SSSP T conditions, the theoreticalyield of grafted benzoate is 100%. FTIR spectra (FIG. 2, discussedabove) confirms the formation of carbonyl functionalized PP via SSSP.

The present invention not only provides a route to PP functionalizationimpossible via melt processing, but also provides a route to preparefunctionalized PP while suppressing β-scission and the resultingmolecular weight reduction. The mechanism for β-scission andcorresponding molecular weight reduction are illustrated in Scheme 4.β-scission is highly dependent on temperature: as processing temperatureincreases (e.g., via melt processing), the extent of β-scissionincreases dramatically. (See, Dickens, B. Journal of Polymer Science:Polymer Chemistry Edition 1982, 20, 1169 1183; Borsig, E.; Hrckova, L.;Fiedlerova, A.; Lazar, M.; Ratzsch, M.; Hesse, A. Journal ofMacromolecular Science, Part A: Pure and Applied Chemistry 1998, 35,1313-1326; and Tzoganakis, C.; Vlachopoulos, J.; Hamielec, A. E.Engineering 1988, 28.) Utilizing near-ambient temperature conditionsassociated with SSSP, the present invention can suppress β-scission andmolecular weight reduction.

Table 1, below, summarizes levels of carbonyl functionalization, as wellas percent reduction in weight average molecular weight (M_(w)) forthese samples. (Reference is made to Tables 2 and 3 in the Examples formore complete data.) As discussed more fully below, the extent ofmolecular weight reduction was approximated from oscillatory shearrheology data using the relationship between zero shear rate viscosity(η_(o)) and weight average molecular weight (M_(w)) for an entangled andmonodisperse polymer, η_(o)˜M_(w) ^(3.4), (See Fox, T. G.; Flory, P. J.Journal of Physical and Colloid Chemistry 1951, 55, 221-234; Ferry, J.D. Viscoelastic Properties of Polymers; Wiley: New York, 1980 p. 641.)The product of SSSP was first annealed under vacuum and at 60° C. inorder to remove any undecomposed BPO that could cause additionalmolecular weight reduction during melt processing after SSSP.Oscillatory shear rheology data were collected at 180° C. and with a 10%strain (using 25 mm parallel discs) after the annealed sample had beenconsolidated into a 25 mm disc. Listed in Table 1 below are the η_(o) ofas received neat PP pellets and 2 samples of carbonyl functionalized PP.The extent of weight average molecular weight reduction was determinedrelative to that of the neat PP from which the samples were made.

TABLE 1 Molecular weight reductions, grafting levels, and graftingyields observed for pulverized samples of ester functionalized PP(PP-g-ES) Mw Grafting Grafting Reduction level Yield Sample (%) (wt %)(%) Neat PP - SSSP 3 — — PP-g-ES/1 20 0.22 87 PP-g-ES/2 29 0.33 65PP-g-ES/3 36 0.46 61

Rheology data presented, herein, are based on samples that were annealedunder vacuum at 50° C. During this process, much of the undecomposed BPOwas removed by vacuum suction. However, as a result of the temperaturethat is utilized, there is potential for some of the BPO to decomposeand produce radicals that engage in chain transfer with the PP; thiswill result in additional molecular weight reduction. There is anopportunity to control the extent of molecular weight reduction thatoccurs as a result by post-pulverization chain transfer caused by BPOthat decomposes after pulverization. This can be achieved by varying thetemperature at which the powdered SSSP product is annealed under vacuum.By decreasing the temperature, the rate of BPO decomposition will bedecreased, thus decreasing the extent of molecular weight reduction. Forexample, if the powdered SSSP product is annealed under vacuum at roomtemperature the undecomposed BPO will be lost via sublimation withoutundergoing significant decomposition to form radicals that could thencause molecular weight reduction of the PP when the radicals engage inchain transfer with the polymer. There is also the possibility ofdirectly melt processing the product of SSSP either by attaching amelting apparatus to the pulverization apparatus or by melting in anentirely separate equipment after pulverization. This will, however,result in the formation of carbonyl functionalized PP with greatermolecular weight reduction (due to the activity of BPO that remainsundecomposed after pulverization).

When a polymer is subjected to extended periods of high temperatureprocessing the viscosity of the polymer decreases with time due tothermal degradation. To study this effect, transient step ratemeasurements were collected using 25 mm cone and plate fixtures, with a0.01 s⁻¹ rate, at 180° C., and using compression molded discs ofsamples. FIG. 3 below shows viscosity as a function of time for neat PPpellet (as received) and neat PP (pulverized). The decrease in viscosityover time is clearly observed for both samples shown in FIG. 3. Incontrast, a sample of 1 wt % BPO pulverized with PP (for whichsignificant levels of carbonyl functionalization of PP was observedafter purification) shows an increase in viscosity with time; this isshown clearly in FIG. 4. This suggests that the carbonyl functionalizedPP is set up to undergo reactions at elevated temperatures; thesereactions then cause the increase in viscosity. The increase inviscosity is likely a result of (but not limited to) branching, which ispossibly caused by, but not limited to, ether formation during elevatedtemperature processing.

EXAMPLES OF THE INVENTION

The following non-limiting example and data illustrate various aspectsand features relating to the methods of the present invention, includingthe preparation of functionalized polymers as are available through thesynthetic methodologies described herein. In comparison with the priorart, the present methods provide results and data which are surprising,unexpected and contrary thereto. While the utility of this invention isillustrated through the use of several polymer components and organicperoxide components which can be used therewith, it will be understoodby those skilled in the art that comparable results are obtainable withvarious other polymers and peroxides, as are commensurate with the scopeof this invention.

Materials. Polypropylene (Total Petrochemicals; MFI=1.5 g/10 min; ASTMstandard D-1238 at 230° C./2160 g load; reported by the supplier) wasused as received. Benzoyl peroxide was used as received (SigmaAldrich).Xylene, octadecyl acrylate (ODA), and 1-pyreneacetic acid (Pyr-AA) wereused for characterizing grafting degrees and reactivity of the PP-g-ESand were used as received (SigmaAldrich). A phenolic antioxidant,Songnox 6260 (Songwon), was used as received in samples made forrheological characterization.

Example 1

Synthesis of PP-g-ES with SSSP. The PP and BPO were pulverized using arelatively harsh screw design at 200 rpm screw speed and 100 g/hr feedrate. The pulverizer was a pilot-plant/research scale Berstofftwin-screw extruder (screw diameter=25 mm, length/diameter=26.5)modified with a cooling system (a Budzar Industries WC-3 chilleroperating at −6° C.); the same apparatus was used in previous SSSPstudies. (It should be noted that the T of the solid-state polymer inthe pulverizer may, at various locations, exceed room temperature byseveral tens of degrees and be warm to the touch upon exiting thepulverizer.) Samples of PP-g-ES were prepared by SSSP using 0.5 to 6.0wt % BPO in the feed. A PP-g-ES sample prepared with 3 wt % BPO was alsoprepared by melt mixing for 10 min at 200° C. with an Atlas ElectronicDevices MiniMAX molder (cup-and-rotor mixer) at maximum rotor speed andwith three steel balls in the cup to provide chaotic mixing. Table 2shows sample composition and process methods.

TABLE 2 Variables for Sample Composition, Processing Method, andCharacterization of benzoate grafting degrees, crystallinity, andtensile properties for neat PP and PP-g-ES samples made via SSSP Young'sYield Amount of Processing Grafting Degree^(a) Grafting Modulus StrengthSample BPO Added (wt %) Method (wt %) (mol %)^(b) Yield (%)Crystallinity (%) (MPa) (MPa) Neat PP pellets — — — — 45 1250 ± 80 36 ±1 (as received) Neat PP — SSSP — — — 44 1170 ± 60 35 ± 1 (after SSSP)PP-g-ES/1 0.5 SSSP 0.22 0.08 87 41 1270 ± 30 36 ± 1 PP-g-ES/2 1.0 SSSP0.33 0.12 65 42 1190 ± 30 34 ± 1 PP-g-ES/3 1.5 SSSP 0.46 0.18 61 41 1130± 30 32 ± 1 PP-g-ES/4 3.0 SSSP 0.81 0.30 52 42 1190 ± 60 32 ± 2PP-g-ES/5 6.0 SSSP 1.14 0.41 36 40 1080 ± 40 29 ± 1 PP-g-ES/4MM 3.0 Melt— — — — — — Mixing ^(a)Grafting degree can also be expressed in μeq(i.e., micromoles of benzoates in 1 g of PP-g-ES) by simplestoichiometric calculations (e.g., 0.22 μeq is equivalent to 0.18 wt %benzoate grafted onto PP). ^(b)Functionalization in mol % represents thenumber of moles of benzoates per mole of repeat units.

Example 2

Purification of PP-g-ES. To ensure high purity and the absence ofcontaminants, PP-g-ES samples employed for quantification of carbonylgrafting, contact angle measurements, and demonstration of reactivitywere purified to remove unreacted BPO by dissolution in boiling xylenefollowed by precipitation with methanol. The samples were dried undervacuum at 70° C. for 24 hr. The PP-g-ES samples for rheology werepurified using a variety of methods that combined washing with acetoneand annealing under vacuum; samples were annealed either at room T for96 hr or at 50° C. for 48 hr. For each annealing condition, two sets ofsamples were studied: one set was washed with acetone before annealingand the other was not washed before annealing. For the washing step, 100g PP-g-ES was stirred in 300 mL acetone for 3 hr at room T; the PP-g-ESwas then removed by filtration. The PP-g-ES samples used in high-T gelpermeation chromatography (high-T GPC) and physical and mechanicalproperty characterization were purified by washing with acetone andannealing at 50° C. for 48 hr.

Sublimation and decomposition occur simultaneously during the annealingprocess; the rate of decomposition increases with increasing T, whilethat of sublimation decreases with increasing T. Because BPOdecomposition could lead to additional MW reduction, its removal bysublimation is preferred in cases where MW reduction must be minimized.Approximations of the time required to remove excess BPO by sublimationcan be determined using the equation for the rate of sublimation:dm/dt=Pα[M/(2πRT)]^(1/2) where dm/dt is change in mass per unit time perunit area, P is the vapor pressure of the solid, α is a vaporizationcoefficient (α=1 in vacuum), M is molecular weight, R is the ideal gasconstant, and T is absolute temperature. Thus, one can control therelative extents of sublimation and decomposition by varying annealing Tand time. For example, by decreasing the annealing T, sublimation willbe become the dominant of the two process though more time will berequired to remove the same amount of BPO.

Example 3

Quantification of Carbonyl Grafting. In order to create a calibrationcurve, ODA/PP blends were prepared by melt processing at 200° C. in aMiniMAX molder for 10 min and at maximum rotor speed with three steelballs in the cup in order to provide chaotic mixing. Blend products werecompression molded into thin films (˜0.3 mm thick) for Fourier transforminfrared (FTIR) spectroscopy using a PHI hot press coupled with a PHIcold press. Octadecyl acetate was chosen because of its structuralsimilarity to PP-g-ES. For each blend, three sets of FTIR data werecollected with 64 scans and 4 cm⁻¹ resolution. Purified PP-g-ES sampleswere compression molded into thin films (˜0.3 mm thick) and tested underthe same conditions as ODA/PP blends.

Example 4

Rheological Measurements. Neat PP and PP-g-ES samples were tested with0.5 wt % Songnox 6260 added to each sample to prevent thermaldegradation. Samples were compression molded into discs devoid ofbubbles using PHI presses. Small amplitude oscillatory shear data werecollected at 180° C., with 2% strain over a frequency range of 0.01 to100 rad/s (measuring from high to low frequency), using astrain-controlled Rheometrics Scientific ARES rheometer equipped with 25mm parallel plates.

Example 5

Physical and Mechanical Properties. Thermal analysis employed a MettlerToledo differential scanning calorimeter (DSC 822e). Samples were heatedat 40° C./min to 200° C., held at 200° C. for 5 min, cooled at 40°C./min to 40° C., held at 40° C. for 3 min, heated at 10° C./min to 200°C., held at 200° C. for 5 min, and cooled at 10° C./min to 40° C. Thecrystallinity was determined from the final cooling step.

Films with ˜0.7 mm thickness were prepared by pressing in a PHI hotpress at 200° C. for 5 min and then rapidly cooling in a PHI cold pressfor 15 min. Tensile specimens were prepared according to ASTM D1708;dumbbell-shaped specimens were cut from films using a Dewes-Gumbs die.An MTS Sintech 20/G (100 kN load cell; crosshead speed=5 cm/min) wasused to obtain Young's modulus and yield strength values at room T.

Example 6

Contact Angle Measurement.Neat PP and PP-g-ES samples were compressionmolded into thin films (˜0.3 mm thick) with smooth surfaces using a PHIhot press at 200° C. for 5 min and then rapidly cooling in a PHI coldpress for 10 min. The static contact angle of a droplet of deionizedwater (5 μL) on the surface of each disc was determined using a KRUSDrop Shape Analysis System, DSA 100; results for each sample wereaveraged over 20 measurements. Reported values of contact anglemeasurements have ±1° experimental errors.

Example 7

Demonstration of Reactivity of PP-g-ES with Pyr-AA. 10 g/L PP-g-ESsamples were dissolved in 0.30 g/L solutions of Pyr-AA in xylene.Solutions were held at 130° C. for 4 hr, after which PP-g-ES wasprecipitated with methanol. To remove unreacted Pyr-AA, samples werepurified six times by dissolution in boiling xylene and precipitation inmethanol. Pyrene label fluorescence was measured with a PhotonTechnology International fluorimeter (λ_(exc)=344 nm).

Example 8

Quantitative Characterization of Ester Functionalization Levels onPP-g-ES: FTIR Spectroscopy. FIG. 5 compares FTIR spectra of neat, asreceived PP and a sample containing 5.0 wt % ODA in an ODA/PP blend. Thepeak at 1732 cm⁻¹ is present only for the ODA/PP blend and is associatedwith the ODA ester functional group. The inset in FIG. 5 is the chemicalstructure of ODA. A peak at 841 cm⁻¹, specific to PP and absent for BPO,is used for normalization of each sample spectrum. For spectralanalyses, the data between 1800 and 1600 cm⁻¹ and between 930 and 740cm⁻¹ were deconvoluted into component peaks using a Lorentzian function.This yielded accurate peak intensities while accounting for peakoverlaps and inconsistent baselines between spectra. A calibration curvebased on ODA was determined using[Ester]=0.25(A ₁₇₃₂ /A ₈₄₁)  Eq. 1where [Ester] is the grafting degree and measured in mol % (i.e., molesof benzoate per mole of PP repeat unit) and A₁₇₃₂ and A₈₄₁ are the areasunder the peaks at 1732 and 841 cm⁻¹, respectively. The grafting yieldwas calculated usingGrafting Yield=([Ester]/[BPO]_(o))×100%  Eq. 2where [Ester] is as defined in Eq. 1 and [BPO]_(o) is the initial amountof BPO added during SSSP; both variables were measured in mol %. (Itmust be noted that if each of the two benzoyloxy radicals resulting fromthe dissociation of BPO were to be grafted to PP, then the graftingyield would be 200%. Of course, for this to occur, all PP radicals wouldhave to be generated solely by chain scission accompanying SSSP, withoutany chain transfer reactions. Chain scission has been shown to accompanySSSP of PP, albeit at quite limited levels, under harsh pulverizationconditions and decreasing with decreasing levels of work done on the PPduring SSSP.) Grafting degrees and yields of PP-g-ES samples weredetermined using Eqs. 1 and 2 and are reported in Table 2; graftingdegrees are presented in both mol % and wt %.

Example 9

As discussed above, FIG. 2 compares the FTIR spectra of PP-g-ES/4,PP-g-ES/4MM, and neat PP pellets and confirms the presence of a strongabsorbance peak for PP-g-ES/4 at 1720 cm⁻¹ and the absence of thisabsorption for the melt processed sample (see FIG. 2a ). As explained,this peak is associated with ester functional groups; the slight shiftof this peak to a lower wavenumber (as compared to the ester peakobserved for ODA) is expected for aromatic esters. FIG. 2b shows anabsorbance at ˜740 cm⁻¹ for PP-g-ES/4. This absorbance is associatedwith phenyl group attachment to the PP backbone and is absent forPP-g-ES/4MM, which confirms that no significant functionalization of anester or addition of a phenyl group can be achieved using BPO via high Tmelt processing. The absence of functionalization during melt processingcan be understood from the T dependence of BPO dissociation intoradicals.

Example 10

Reference is made to Table 2, above. As compared to grafting yieldsreported in the literature for PP-g-ES synthesized with peroxyesters andunsaturated peroxides at 160-180° C. and in an inert environment, the 36to 87% grafting yields (corresponding to 0.41 to 0.18 mol % graftingdegrees, respectively) obtained during PP-g-ES synthesis via SSSP in anair environment are significantly higher. (Assoun et al. reported ˜17%(and 0.02 mol %) as the largest grafting yield for a series ofperoxyesters used for PP functionalization by melt extrusion at 180° C.and in an N₂ environment; Saule et al. reported a grafting yield of 5%for isotactic PP grafted in a 2.5 hr batch process carried out in aninert environment at 160° C. using a peroxyester. For a series ofunsaturated peroxides, which were expected to significantly improvegrafting yields in PP, Saule et al. reported a maximum grafting yield of˜40%.) It is evident from these comparisons that PP-g-ES synthesis fromBPO via SSSP results in improvement in both grafting degree and graftingyield over the PP-g-ES counterparts that were prepared at elevated Tusing asymmetric peroxyesters.

Example 11

PP-g-ES MW Reduction as a Function of BPO Purification Method: RheologyCharacterization. Rheology is used to evaluate the change in PP M_(w)caused by benzoate functionalization and consider the effect of themethod used to purify the PP-g-ES of unreacted BPO and its byproducts.Before discussing such characterization of M_(w) in detail, it isimportant to note that some samples did not exhibit the presence of aη_(o) regime in the rheology data. Instead, even at the lowestfrequency, |η*| was increasing with decreasing frequency. This behavioris believed to be associated with long-chain branching. Examples fallinto two classes: 1. PP-g-ES/2 and PP-g-ES/3 that were not subjected toany purification prior to rheological testing; and 2. PP-g-ES/4 andPP-g-ES/5 that were subjected to all levels of purification, whichindicates that these samples, with the highest ester functionalizationlevels, were branched coming out of the SSSP apparatus.

Neat PP after SSSP had η_(o) that was 10% lower than that of neat PPpellets (i.e., η_(o)=28,500 Pa·s for neat PP after SSSP), indicating a3% reduction in M_(w). Thus, in the absence of BPO, SSSP causes nearlynegligible MW reduction of neat PP. For PP-g-ES/1 (0.08 mol % graftlevel and 87% grafting efficiency) that was characterized directly asthe output from the pulverizer without any purification step to removeunreacted BPO, η_(o) was reduced by ˜61% relative to neat PP pellets,indicating a 24% reduction in M_(w). This M_(w) reduction is similar tothe 24% reduction measured by Assoun et al. for a PP-g-ES sample made bymelt processing and asymmetric peroxy molecules which had only 0.02 mol% functionalization, one fourth that of our PP-g-ES/1 sample. When thesame PP-g-ES/1 sample was subjected to various purification steps, theapparent reductions in M_(w) from zero shear rate viscosity data were11-12% (unwashed or washed with acetone, followed by room T annealingunder vacuum for 96 hr) and 20-21% (unwashed or washed with acetone,followed by annealing at 50° C. under vacuum for 48 hr). The resultsindicate that at low functionalization levels only very small amounts ofβ-scission leading to MW reduction occur during SSSP; this is also trueeven during post-SSSP annealing or processing under conditions thatwould lead to decomposition of unreacted BPO into radicals (i.e.,annealing at 50° C.).

At moderate functionalization, PP-g-ES/2 and PP-g-ES/3 with 0.12-0.18mol % ester, which require higher BPO levels in the feed, linear chainbehavior is evident from rheology for all purification conditions exceptno purification. This implies that the PP-g-ES output from thepulverizer is linear in nature and only becomes branched if substantiallevels of covalently attached benzoates and undecomposed BPO are presentin the sample at the time it is subjected to melt processing. Based onη_(o) values, M_(w) was reduced relative to neat PP by 23-25% and 27-28%in PP-g-ES/2 and PP-g-ES/3 for samples (washed with acetone or unwashedand) annealed at room T under vacuum for 96 hr and by 30% and 36% inPP-g-ES/2 and PP-g-ES/3 for samples (washed with acetone or unwashedand) annealed at 50° C. under vacuum for 48 hr. While these values ofM_(w) reduction are not negligible, they are far below the 53 to 70%reductions reported by Saule et al., who did post-polymerization esterfunctionalization of PP by melt processing with asymmetric peroxymolecules.

Example 12

High-T GPC Characterization of PP-g-ES and Chain Scission Events Per PPRepeat Unit. High-T GPC data were obtained for neat PP pellets and thelinear PP-g-ES/1, PP-g-ES/2, and PP-g-ES/3. Molecular weight averageswere evaluated by high-T GPC (at 145° C. with trichlorobenzene as eluentand triple-detection) at the Polymer Characterization Lab at theUniversity of Tennessee, Knoxville, Tenn. 37996. In order to draw acomparison that reflects chain scission that could occur during thepurification process, an evaluation was conducted of those samples thathad been washed with acetone and annealed at 50° C. under vacuum for 48hr and which showed larger reductions in η_(o) than samples that hadbeen annealed at room T for 96 hr. Samples were dissolved intrichlorobenzene and tested at 145° C.; data from a triple detectionmethod were used.

It is noted that data associated with triple detection provided theworst case scenario for percent reductions in MW as compared to datafrom other detection methods. Using trichlorobenzene as solvent, GPCsamples were run at 145° C. and analyzed with light scattering, tripledetection, and universal calibration. The standard deviation of MW datafrom universal calibration, light scattering, and triple detection is19,000 g/mol for M_(n) and 17,000 g/mol for M_(w). Percent reductions inM_(n) and M_(w) were highest for triple detection data for all PP-g-ESsamples. For light scattering the following values were obtained:PP-g-ES/1 (9 and 22% reductions in M_(n) and M_(w), respectively),PP-g-ES/2 (3 and 23% reductions in M_(n) and M_(w), respectively), andPP-g-ES/3 (14 and 34% reductions in M_(n) and M_(w), respectively). Foruniversal calibration the following values were obtained: PP-g-ES/1 (10and 16% reductions in M_(n) and M_(w), respectively), PP-g-ES/2 (12 and25% reductions in M_(n) and M_(w), respectively), and PP-g-ES/3 (13 and29% reductions in M_(n) and M_(w), respectively). Averaged across allthree detection methods, the following M_(n) and M_(w) values wereobtained for neat PP pellets (M_(n)=142,200 g/mol and M_(w)=585,100g/mol) and resulted in percent reductions in M_(n) and M_(w) aredetermined as 6-18% and 21-33%, respectively for PP-g-ES samples.

Average MW values, as well as percent reduction in number average MW(M_(n)) and percent reduction in M_(w), for these samples are presentedin Table 3. The percent reductions in M_(w), as determined from high-TGPC, are in good agreement with those determined from rheology (seeTable 3). As expected, the percent reduction in M_(w) is greater thanthe corresponding percent reduction in M_(n) for each sample. This isbecause the probability that a chain undergoes scission increases as thechain length increases thereby resulting in a greater reduction in M_(w)than M_(n).

The average number of scission events per chain can be determined fromthe M_(n) data:z _(c) =[M _(n,o) /M _(n,f)]−1  Eq. 3where M_(n,o) is the initial M_(n), and M_(n,f) is the final M_(n) afterscission (and purification). Based on Eq. 3, z_(c)=0.10 scission eventsper chain for PP-g-ES/1, i.e., for every 100 original PP chains, therewere 10 scission events. If we assume that each scission event resultedin the formation of a radical at each chain end, then we can expect atotal of 20 benzoates to be grafted onto 110 PP chains. However, basedon the 104,900 g/mol M_(n) and 0.08 mol % grafting degree for PP-g-ES/1,we determine that ˜2 benzoates are grafted per chain. Thus, for 110chains, PP-g-ES/1 contains ˜220 grafted benzoates, a factor of 11 morethan the number of chain ends created. This indicates that the vastmajority of benzoates are grafted along the PP backbone and not only atchain ends, that little of the benzoate grafting is due to reaction ofbenzoyloxy radicals with PP radicals formed by chain scissionaccompanying SSSP, and that the limit for grafting yield during SSSP (asdefined by eq. 2) is at most slightly above 100%. This also providesfurther proof that during SSSP, PP macroradicals are less likely toundergo β-scission, thus allowing for benzoate functionalization alongthe PP backbone. Using similar analyses, z_(c) and the number ofbenzoates per chain for PP-g-ES/2 and PP-g-ES/3 were determined and areshown Table 3. For both PP-g-ES/2 and PP-g-ES/3, the number of benzoatesgrafted onto the PP chain vastly exceeds what would have been expectedif the benzoyloxy radical only terminated with PP macroradicals producedas a result of chain scission accompanying SSSP.

With z_(c)=0.10 for PP-g-ES/1 and PP-g-ES/2 and noting thatM_(n,o)=115,000 g/mol for the neat PP starting material, it wasdetermined that one scission event happens every 26,100 repeat units. Asimilar calculation indicates that one scission event happens every12,400 repeat units in the synthesis (and purification) of PP-g-ES/3.For PP-g-ES syntheses by Saule et al. at 160° C. in inert environmentsand resulting in 30-40% grafting yields, we calculate that there was onescission event per 1000-2000 repeat units. Thus, PP-g-ES synthesis bySSSP results not only in higher grafting yield (62 to 87% for PP-g-ES/1,PP-g-ES/2, and PP-g-ES/3) but also in a factor of ˜10 lower frequency ofscission events as compared to PP-g-ES prepared by Saule et al.

For the PP-g-ES sample with only 0.02 mol % ester functional groupsynthesized by Assoun et al. by melt processing in an inert environment,it was calculated that one scission event occurred for every 11,800repeat units. In comparison with PP-g-ES/1 (prepared with similarperoxide feed composition of ˜0.1 mol %), the PP-g-ES prepared by Assounet al. showed not only a much lower grafting degree as compared to itsSSSP counterpart (0.08 mol % grafting degree and one scission event per26,100 repeat units) but also a factor of 2 higher frequency of chainscission. Thus, relative to post-polymerization synthesis by meltprocessing, PP-g-ES synthesis by SSSP results in enhanced graftingdegree and yield and in a major reduction in the frequency of chainscission events per repeat unit, which in turn causes MW reduction.

TABLE 3 MW characterization before and after functionalization via SSSPusing oscillatory shear rheology and high-T GPC Grafting Rheology High-TGPC Degree Percent M_(w) Percent M_(n) Percent M_(w) Ester groups Sample(mol %) η_(o) (Pa · s) reduction^(a) (%) M_(n) (g/mol) reduction (%)M_(w) (g/mol) reduction (%) z_(c) per chain Neat PP — 31,800 — 115,000 —585,300 — — pellets (as-received) PP-g-ES/1 0.08 14,800 20 104,900 9439,800 20 0.10 2 PP-g-ES/2 0.12 9,900 29 104,400 9 422,800 29 0.10 3PP-g-ES/3 0.18 7,100 36 95,400 17 376,000 36 0.21 4 ^(a)Percentreduction in M_(w) relative to neat PP pellets (as received) wascalculated using the assumption that η_(o) scales with M_(w) to the 3.4power

Example 13

Physical and Mechanical Properties. Table 2, above, shows the percentcrystallinity for PP-g-ES samples made by SSSP. Percent crystallinity(χ_(crys)) was determined using Eq. 4:χ_(crys)=(ΔH _(f) /ΔH ^(o) _(f))×100%  Eq. 4where ΔH_(f) is the sample enthalpy of fusion and ΔH^(o) _(f) isenthalpy of fusion for 100% crystalline PP (ΔH^(o) _(f)=207.1 J/g).Within experimental error, it is observed that SSSP of neat PP does notaffect crystallinity. For PP-g-ES samples, there are only slightdecreases in crystallinity relative to neat as-received PP, from 45% to40-42%. This behavior can be explained by the fact that the bulkybenzoate groups grafted onto the PP backbone (and possibly the presenceof PP branches) disrupt crystal formation.

Table 2 also compares Young's modulus (E) and yield strength (σ_(y))values of neat PP before and after SSSP with those of PP-g-ES samples.Within error, SSSP of neat PP had no effect on E and σ_(y), consistentwith the fact that the MW and crystallinity of neat PP before and afterSSSP were little changed or identical within error. The grafting of PPwith 0.08 to 0.30 mol % benzoate by SSSP results in no change E withinerror from the value for neat as-received PP and, at most, only a ˜10%reduction in σ_(y). However, with 0.41 mol % ester functionalization(sample PP-g-ES/5), there is a slightly less than 15% decrease in E anda 20% decrease in σ_(y) relative to neat as-received PP, both outsideexperimental error. These small reductions may be expected as tensileproperties of PP are closely linked to MW and crystallinity, both ofwhich decrease slightly with benzoate grafting and are lowest forPP-g-ES/5.

Example 14

Interfacial Property Modification: Contact Angle Characterization. Inorder to verify the improved wettability and polarity of PP-g-ES samplesas compared to neat as-received PP, contact angles were measured forsessile drops of deionized water placed on the surfaces of smooth neatPP and PP-g-ES films. The contact angle decreases smoothly withincreasing level of ester grafting (data not shown), which is consistentwith the notion that functionalized PP will have improved interfacialadhesion with more polar materials as compared to the parent PP fromwhich it was synthesized. In contrast, the contact angle of neat PPafter SSSP remains unchanged, within error, as compared to the neat, asreceived PP. Thus, the polarity of neat PP is unaffected by SSSPprocessing; this is consistent with observation of the absence ofketonization or carboxylic acid formation from any radical stabilizationby atmospheric oxygen. These results provide further confirmation of theability of SSSP to achieve direct ester functionalization PP using BPOand that PP interfacial properties can be easily tuned via esterfunctionalization by SSSP.

Example 15

Reactivity of PP-g-ES with Pyr-AA. Functionalized polyolefins are oftenused commercially as reactive compatibilizers for immiscible blends. Asfurther proof of functionalization, the reactivity of the PP-g-ESsynthesized by SSSP with Pyr-AA was investigated. Under the conditionsof reaction, transesterification between PP-g-ES and Pyr-AA is expected,resulting in a covalent attachment of pyrenyl moieties to the PPbackbone. The presence of pyrenyl units covalently attached to PP iseasily confirmed by fluorescence spectroscopy.

FIG. 6 compares the fluorescence spectra of a solution of 0.3 g/L Pyr-AAin xylene and a 2.0 g/L PP-g-ES/5 solution in xylene after reaction withPyr-AA (followed by six cycles of dissolution/precipitation to removeany unreacted Pyr-AA). The spectrum for PP-g-ES/5 shows slight shifts inpyrenyl emission peak wavelengths and structure as compared to that forPyr-AA; these shifts have been observed in other studies and areassociated with modification of photophysical responses (e.g., thepolarization, intensity, and energy of the fluorescence transitions)caused by the nature of the chromophore attachment to the polymerbackbone. Nonetheless, the fluorescence observed for PP-g-ES/5 afterreaction with Pyr-AA provides further proof of direct functionalizationof PP with benzoates using BPO only and of the potential utility ofPP-g-ES as reactive compatibilizer in polymer blends. Control studiescarried out on neat PP and PP-g-ES/4MM (synthesized via meltprocessing), using the same reaction and purification protocol as forPP-g-ES/5, resulted in no fluorescence.

In summary, as demonstrated by representative non-limiting embodiments,this invention provides a methodology for direct ester functionalizationof PP using BPO, a symmetric organic peroxide; during SSSP,functionalization is made possible by both thermal and mechanochemicaldecomposition of BPO at the near-ambient processing T. At these Tconditions, the extent of decarboxylation of the benzoyloxy radicalsformed during BPO decomposition is significantly decreased, allowing foreffective functionalization of PP with ester functional groups (i.e.,benzoates), resulting in grafting yields of up to about 87%. Contrary tothe functionalization realized by SSSP processing, the high T conditionsassociated with melt processing result in no grafting for a similarsystem of PP and BPO because of high extents of decarboxylation. Thus,SSSP provides a new platform of chemistries, which are not attainablevia melt processing, for direct functionalization of PP with benzoates.

In addition to achieving PP functionalization with benzoates using BPO,we also demonstrated that this functionalization can be attained withlimited reductions in M_(n) and M_(w); for PP-g-ES with 0.18 mol %benzoate groups, only one chain scission event happens for every 12,400repeat units, resulting in a 17% reduction in M_(n) and a 36% reductionin M_(w). These moderate MW reductions are achieved because of the lowprocessing T employed during SSSP. Under the high T conditions utilizedwith melt processing, the extent of β-scission, the primary cause of MWreduction, is high. By processing via SSSP, we strongly suppress theextent of β-scission and thus suppress MW reduction that could accompanyfunctionalization.

Using contact angle measurements and based on a transesterificationreaction with Pyr-AA, we provided further proof of successful polarfunctionalization of PP. We showed that the contact angle of a dropletof deionized water decreased with grafting degree, proving an increasein polarity for PP-g-ES samples relative to the neat, parent PP.Transesterification of PP-g-ES with a fluorescent chromophore was usedto demonstrate potential in reactive compatibilization. Finally, thelittle to no reduction in crystallinity coupled with moderate MWreductions resulted in PP-g-ES samples with little to no losses inmechanical and physical properties relative to the neat parent PP.Together, these results confirm that SSSP can be used to achieve directester functionalization of PP to high grafting yields and without theuse of a polar monomer.

We claim:
 1. A method of functionalizing polypropylene with a benzoyloxymoiety, said method comprising: providing a mixture comprising a polymercomprising a polypropylene component and benzoyl peroxide; and applyinga mechanical energy to said mixture through solid-state shearpulverization in the presence of cooling at least partially sufficientto maintain said polymer in a solid state during said pulverization,said pulverization at least partially sufficient to graft a benzoyloxymoiety onto said polypropylene component, said pulverization providing abenzoyloxy-functionalized polymer.